Synthetic polymeric fibers that have physical and morphological characteristics generally similar to pulp fibers produced from natural woods have been known for approximately 10 years. Examples of such fibers are the synthetic wood pulp fibers formed of polyethylene that are sold by Crown Zellerbach under the trademark SWP.
Various methods of making synthetic wood pulp fibers are known, including (1) solution polymerization accompanied by stirring, (2) dissolving a preformed polymer and subjecting the solution to an anti-solvent, or (3) forming the polymer at the interface between liquid layers, with localized stirring provided to pull the polymers thus formed into fibrillated forms. Examples of methods of producing synthetic wood pulp fibers are disclosed in U.S. Pat. Nos. 3,560,318; 3,081,519; 3,003,912; 3,068,527; and 3,290,207; South African Pat. No. 697,432; United Kingdom 1,102,342; and Netherlands Patent Application A132/48-7313178.
As used in this specification and the appended claims, the term "synthetic wood pulp fibers" means synthetic, water dispersible, thermoplastic, elongated, supple, randomly bent, polymeric fibers or fibrils generally similar in size and shape to conventional wood pulp fibers produced from naturally occurring woods. Each such "synthetic wood pulp fiber" is of irregular cross sectional shape measured at any given point along its length, and in addition is nonuniform in cross section along its length. The predominant shape of the fibers is usually rather ribbon-like.
The present invention utilizes synthetic wood pulp fibers in a high loft, low density, nonwoven fibrous material, such as an air-laid web, which is one component of a wipe, swab, or other similar cleaning device. Cleaning devices of this type should possess two characteristics, both of which are important but which are mutually inconsistent First, the device must have a substantial amount of wet strength in order to hold the desired shape and avoid disintegration of the fibrous material when in use. This characteristic is best provided by a compactly assembled aggregation of fibers bonded with an adhesive binder. Second, the cleaning device must have a high degree of liquid absorbency, as well as a substantial amount of resiliency in its structure in order to be most efficient in adapting to corners to be cleaned. This characteristic is best provided by a high loft, low density, nonwoven fibrous material in which the fibers are loosely assembled.
The two contradictory objectives just described can be achieved by joining nonwoven webs of different types to form the desired cleaning device. Thus, a wet-laid nonwoven web of compactly assembled fibers bonded with a water insoluble adhesive binder can be used to provide the necessary wet strength. An air-laid nonwoven web of loosely assembled fibers can be used to provide the high loft, low density, liquid absorbent layer.
Use of such different fibrous layers to form the two-ply cleaning device of this invention presents difficulties in causing the two layers to adhere to each other without destroying the liquid absorbent character of the second layer. These difficulties are suprisingly avoided by the present invention.